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双酚A(BPA)是工业生产中广泛使用的原材料之一,主要应用于各种塑料日用品的制造过程中. 近年来,在污水处理厂出水、再生水以及各类自然水体中,均检出了BPA等内分泌干扰物的存在[1],因容易“致畸致癌致突变”,BPA的存在带来了潜在的生态健康风险. 目前,吸附法[2]、膜分离法[3]等方法已被用于BPA废水的处理. 但上述方法通常存在去除速率低、再生污染较大等缺点. 因此研发针对BPA的高效环保的处理手段具有重要意义.
光催化技术的反应条件相对温和,可在常温常压下进行,且对有机物的降解比较完全,该技术已被证明可用于BPA的处理[4]. 在诸多可见光催化材料中,石墨相氮化碳(g-C3N4,CN)作为一种二维非金属半导体,因其具有较好的可见光吸收能力、热稳定性、化学稳定性和独特的电子结构,受到越来越多的关注[5]. 为进一步提升CN的可见光催化活性,已发展出的改性手段包括金属负载[6]、掺杂改性[7]、形貌调控[8]和构建异质结[9]等.
目前,研究者们对CN的金属修饰已有诸多研究,其中金属钴(Co)以单原子掺杂、化学键键合、表面颗粒负载等多种方式应用于催化材料的构建中. Zhou等[10]通过实验和模拟研究了Co掺杂浓度对 g-C3N4光学性能的影响, 质量分数0.15 %Co掺杂g-C3N4在450—800 nm波长范围内具有较好的吸收特性,展现出优异的光吸收和电导性能. Bhagat等[11]引入Co和B共掺杂的g-C3N4,因Co—B间的作用力引起了电荷重排,改变了N位的电荷分布,使得该复合催化剂表现出较好的光催化性能. Zheng等[12]设计了一种新型的Co3O4@CoO/g-C3N4三元复合催化剂, g-C3N4超薄纳米片均匀地分散在钴氧化物的花状微米粒子上,促进了光诱导电荷的分离,使该复合催化剂具有良好的氧化还原活性,可作为光催化剂降解四环素.
虽然多种钴物种已被证实可用于CN的修饰,但目前的改性方式多为分步操作,且钴源多为无机钴盐类,如何利用有机钴源,结合有机官能团与CN碳氮前驱体的相互作用,调变CN的聚合过程,一步实现钴修饰CN材料的制备仍有待研究. 研究表明,乙酰丙酮铁在碳化后会在材料表面形成铁氧纳米颗粒[13],而金属氧化物颗粒往往可作为催化反应的活性位点,进而提高催化反应速率. 钴与铁同为第Ⅷ主族的过渡金属元素,常用于构建石墨相氮化碳材料的活性位点.
本研究以尿素和乙酰丙酮钴为原料,通过一步热聚合法成功制备出超分散钴修饰多孔石墨相氮化碳(xCoCN)催化剂,并将其用于模拟太阳光下催化降解BPA,其主要研究内容如下:
(1)制备出含有不同比例钴物种修饰的CN光催化剂(xCoCN),并对催化剂进行了化学结构与形貌、光电性质的表征和分析.
(2)研究xCoCN催化剂光催化降解BPA的性能,探讨光催化降解BPA的性能提升的原因以及钴物种作为助催化剂的作用. 探讨了催化剂用量、BPA的初始浓度和初始pH值对反应的影响,进一步研究了xCoCN光催化剂的稳定性. 揭示了xCoCN光催化降解BPA过程中的活性物种,探讨了可能的降解路径.
超分散钴修饰多孔石墨相氮化碳光催化处理水中双酚A
Photocatalytic degradation of BPA in water by superdispersed cobalt-modified porous graphite phase carbon nitride
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摘要: 本文通过一步热聚合法,以尿素和乙酰丙酮钴为前驱体,设计和制备了钴物种修饰的多孔石墨相氮化碳光催化剂(xCoCN). 利用透射电子显微镜(TEM)、X射线衍射(XRD)、傅里叶红外光谱(FTIR)、X射线光电子能谱(XPS)、BET比表面积测试、电化学阻抗(EIS)、紫外可见漫反射(UV-vis DRS)等手段对所得xCoCN催化剂进行表征分析,并以水中双酚A(BPA)为目标污染物,考察了xCoCN的光催化活性以及pH、催化剂用量、BPA浓度等实验条件对催化性能的影响. 通过活性物种捕获实验探究反应机制,实验结果表明,在模拟太阳光照射下,5CoCN用量为0.4 g·L−1时,3 h内对15 mg·L−1 双酚A的光催化降解率达86.6%,通过活性物种捕获实验确定了空穴和超氧自由基为主要的活性物种. xCoCN光催化活性较CN有明显提升,这归因于钴物种的引入在CN表面提供了更多的活性位点,提高了电子空穴对的分离效率.Abstract: In this paper, a cobalt species-modified porous graphite-phase carbon nitride photocatalyst (xCoCN) was designed and prepared by one-step thermal polymerization, using urea and acetylacetone cobalt as the precursor. The xCoCN catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), fourier transform infrared (FT-IR), X-ray photoelectron spectrum (XPS), BET ratio surface area test and electrochemical impedance spectroscopy (EIS). Bisphenol A (BPA) was used as the target pollutant, and the effects of the photocatalytic activity of xCoCN and pH, catalyst dosage and BPA concentration were investigated. The reaction mechanism was also explored through the active species capture experiments. The results showed that when the dosage of 5CoCN was 0.4 g·L−1 under simulated sunlight, the photocatalytic degradation rate of 15 mg·L−1 BPA reached 86.6% within 3 hours. h+ and ·O2- were identified as the major active species by active species capture experiments. The enhanced photocatalytic activity of xCoCN as compared to graphitic carbon nitride (CN) is attributed to the introduction of cobalt species in the CN surface modification that provided more active sites and improved the separation efficiency of electron hole pairs.
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Key words:
- Graphitic carbon nitride /
- photocatalysis /
- bisphenol A /
- cobalt species modification.
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图 7 (a)不同投加量的5CoCN对BPA光催化降解曲线(b)反应速率常数k变化曲线(c)不同初始浓度的BPA光催化降解浓度变化曲线(d)反应速率常数k变化曲线
Figure 7. (a) Photocatalytic degradation curve of BPA with different dosage of 5CoCN (b)Curve of reaction rate constant k (c) Photocatalytic degradation curve of photocatalytic degradation of BPA with different initial concentrations (d) Curve of reaction rate constant k
表 1 5CoCN各元素组分比例(%)
Table 1. Element proportion in 5CoCN from EDS analysis (%)
元素
Element质量
Mass原子
AtomC 45.78 50.42 N 50.53 46.93 O 3.10 2.52 Co 0.59 0.13 总计 100.00 100.00 表 2 基于C 1s谱图计算的不同形态C原子含量(%)
Table 2. The content of C atoms in different forms calculated based on the C 1s spectrum (%)
C=C C=O N=C—N π激发氮 CN 30.45 0 56.03 13.52 5CoCN 20.83 7.33 59.48 12.45 -
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